Required Formulas Flashcards by Alexa Carnahan

Percentage strength - % w/v =

X g / 100mL

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Percentage strength - % v/v =

X mL / 100mL

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Percentage strength - % w/w =

X g / 100g

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Ratio strength - percentage strength =

100 / ratio strength

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Ratio strength - ratio strength =

100 / percentage strength

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Parts per million (PPM)

PPM –> percentage strength - move decimal left 4 places
percentage strength –> PPM - move decimal right 4 places

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Specific gravity (SG) =

weight of substance (g) / weight of equal volume of water (g)
or
SG = g / mL

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Dilution and concentration (changing strength or quantity)

Q1 x C1 = Q2 x C2
Q1 = old quantity
C1 = old concentration
Q2 = new quantity
C2 = new concentration

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Osmolarity

mOsmol/L = Wt of substance (g/L) / MW (g/mole) x (# of particles) x 1,000

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Isotonicity (E value)

E = (58.5)(i) / (MW of drug)(1.8)

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Moles

mols = g / MW

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Millimoles

mmols = mg / MW

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Milliequivalents

mEq = mg x valence / MW
or
mEq = mmols x valence

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Enteral nutrition calories

carbs, protein = 4kcal/gram
fat = 9kcal/gram

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Parenteral nutrition calories

dextrose monohydrate = 3.4kcal/gram
amino acid solutions = 4kcal/gram
ILE 10% = 1.1 kcal/mL
ILE 20% = 2 kcal/mL
ILE 30% = 3kcal/mL

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Determining fluid needs

when weight >20kg: 1,500mL + (20mL)(weight in kg - 20)
can estimate using 30-40 mL/kg/day

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Total energy expenditure

TEE = BEE x activity x stress factor

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Grams of nitrogen from protein

nitrogen (g) = protein intake (g) / 6.25

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Corrected calcium for albumin <3.5 (not needed with ionized Ca)

Cacorrected (mg/dL) = calciumreported (serum) + [(4.0 - albumin) x (0.8)]

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Body mass index (BMI)

BMI (kg/m2) = weight (kg) / [height (m)]^2
or
weight (lbs) / [height (inches)]^2 x 703

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Ideal body weight (IBW)

IBW (males) = 50kg + (2.3kg)(number of inches over 5ft)
IBW (females): = 45.5 kg + (2.3kg)(number of inches over 5ft)

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Adjusted body weight

AdjBW0.4 = IBW + 0.4(TBW - IBW)

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Which weight to use for drug dosing

all drugs (if underweight): TBW
most drugs (if normal weight or obese): TBW
exceptions:
acyclovir, aminophylline, levothyroxine, theophylline (normal weight, obese): IBW
aminoglycosides (obese): AdjBW0.4

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Flow rates/drop factor (drops/min)

(# drops / mL) x (mL / hr) x (hr / 60min) = # drops / min

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Dehydration

BUN:SCr > 20.1

CrCl

CrCl (mL/min) = [140-(age of pt)] / (72 x SCr) x weight (kg) (x0.85 if female)

Arterial blood gas

ABG: pH/pCO2/pO2/HCO3/O2 sat

pH < 7.35 -->

acidosis

pH > 7.45 -->

alkalosis

Respiratory:

pCO2 < 35 --> alkalosis pCO2 > 45 --> acidosis

Metabolic:

HCO3 > 26 --> alkalosis HCO3 < 22 --> acidosis

Ex. decreased pH + increased pCO2 -->

respiratory acidosis

Ex. decreased pH + decreased HCO3 -->

metabolic acidosis

Anion gap

AG = Na - Cl - HCO3

pH calculations: weak acid

pH = pKa + log[salt/acid]

pH calculations: weak base

pH = pKa + log[base/salt}

Percent ionization: weak acid

% ionization = 100 / [1+10^(pKa-pH)]

Percent ionization: weak base

% ionization = 100 / [1+10^(pH-pKa)]

Absolute neutrophil count

ANC (cells/mm3) = WBC x [(% segs + % bands)/100]

Temperature conversions

C = (F - 32) / 1.8 F = (C x 1.8) + 32

Time to burn

TTB (with sunscreen in min) = SPF x TTB (without sunscreen)

Mean =

average value

Median =

value in middle of an ordered list

Mode =

value that occurs most frequently

Risk =

of subjects in group with an unfavorable event / total # of subjects in group

Relative risk (RR) =

risk in treatment group / risk in control group

Relative risk reduction (RRR) =

(% risk in control group - % risk in treatment group) / % risk in control group

Absolute risk reduction (ARR) =

(% risk in control group) - (% risk in treatment group)

Number needed to treat (NNT) or harm (NNH) =

1 / ARR (expressed as decimal)

Odd ratio

OR = AD / BC A = exposure present, outcome present B = exposure present, outcome absent C = exposure absent, outcome present D = exposure absent, outcome absent

Hazard ratio (HR) =

hazard rate in treatment group / hazard rate in control group

Incremental cost-effectiveness ratio =

(C2 - C1) / (E2 - E1) C = costs E = effects

Pack-year smoking history

pack-year smoking history = cigarette packs / day x years smoking

Initiating basal-bolus insulin in T1DM

1. calculate total daily dose (TDD) of 0.5 units/kg/day using TBW 2. divide into 1/2 basal and 1/2 rapid acting 3. split rapid-acting among meals

Insulin-to-carb ratio: rule of 450 for regular insulin

450 / TDD of insulin = grams of carbs covered by 1 unit of regular insulin

Insulin-to-carb ratio: rule of 500 for rapid-acting insulin

500 / TDD of insulin = grams of carbs covered by 1 unit of rapid-acting insulin

Correction factor: 1,500 rule for regular insulin

1,500 / TDD of insulin = correction factor for 1 unit of regular insulin

Correction factor: 1,800 rule for rapid-acting insulin

1,800 / TDD of insulin = correction factor for 1 unit of rapid-acting insulin

Correction dose for diabetes

[(blood glucose now) - (target blood glucose)] / correction factor = correction dose

Dyslipidemia - friedewald equation

LDL = TC - HDL - (TG/5) do not use TG if TG >400

Nonsterile compounding - minimum weighable quantity (MWQ)

MWQ = sensitivity requirement / acceptable error rate (usually 0.05)

Oncology - body surface area (Mosteller)

BSA (m^2) = square root of [Ht (cm) x Wt (kg)] / 3,600

Bioavailability

F (%) = 100 x (AUCextravascular/AUCintravenous) x (dose intravenous/doseextravascular)

Volume of distribution

Vd = amount of drug in body / concentration of drug in plasma

Clearance

Cl = (F x dose) / AUC or Cl = ke x Vd

Elimination rate constant

ke = Cl / Vd

Predicting drug concentrations

C2 = C1 x e^-kt ke = [ln(C1/C2)] / t

Half-life

t1/2 = 0.693 / ke

Loading dose

LD = (desired concentration x Vd) / F

Mean arterial pressure

MAP = [(2 x diastolic pressure) + systolic pressure] / 3

Seizures/epilepsy - phenytoin (total) correction for albumin < 3.5

Phenytoincorrected (mcg/mL) = (total phenytoin measured) / [(0.2 x albumin) + 0.1]

Required Formulas Flashcards

(71 cards)